LEDs are semiconductor devices that produce light when a current is supplied to them. LEDs are intrinsically DC devices that only pass current in one polarity, and historically have been driven by constant current or constant voltage DC power supplies. When driven by these DC power supplies, LEDs are typically provided in a series string, in parallel strings or in series parallel configurations based on the drive method and LED lighting system design.
Recent advancements in the field of lighting have led to the use of LED circuits which are capable of using AC power to drive LEDs configured in particular devices and/or circuit arrangements such that some of the LEDs may operate during the positive phase of the AC power cycle, some LEDs may operate during the negative phase of the AC power cycle, and, in some cases, some or all LEDs may operate during both the positive and negative phases of the AC power cycle. LEDs powered with AC power typically last substantially longer than traditional halogen and incandescent devices or lamps, and typically require much less power to produce a substantially similar amount of light. However, LEDs powered by AC power sources act as a non-linear load. As a result of the non-linearity, LEDs powered using AC power sources may have a lower power factor, and may have a greater total harmonic distortion, than existing halogen or incandescent lighting devices. Having a low power factor and increased distortion may result in higher energy costs, transmission losses, and/or damage to electrical equipment. While the amount of power needed to drive an LED lighting device may be less than to drive a halogen or incandescent lighting device producing a substantially similar amount of light, the overall cost of operating an LED lighting device using AC power may be equal to or more than the amount required to drive the halogen or incandescent lighting device using the same AC power source.
Another advantage that traditional halogen and incandescent lighting devices have over present LED lighting devices driven with AC power is that halogen and incandescent lighting devises have the ability to change color temperature when the voltage provided to them is changed. Light in halogen and incandescent lighting devices are typically generated by a hot wire filament. As the power provided to the bulb is decreased, the temperature of the filament typically decreases, causing the color temperature of the emitted light to move down the color spectrum and make the light appear warmer, i.e. closer to yellow or amber or red than white or blue. In order to achieve this effect in LED lighting devices driven with AC power, complicated and expensive drive schemes are currently required which drive up the cost of the lighting device and the cost to operate the same. One example would be color mixing with red, green and blue LEDs referred to as “RGB” which typically uses pulse width modulation to create any color of light desired. However, the power supplies for this are very complex and larger in size. Other complex versions of constant current or constant voltage DC with only two different LED colors can also be used, however these power supplies can also be large and complex. These drive schemes may also be inefficient and waste additional power or electricity, further increasing operating costs.
Therefore, it would be advantageous to design a circuit, device, or system utilizing LEDs that maximizes power factor while reducing the total harmonic distortion resulting from driving the circuit, device or system using AC power.
It would also be advantageous to design a circuit, device, or system where the color temperature of the LEDs driven with AC power may be dynamically adjusted using simple control methods without having to utilize any complicated or expensive drive mechanisms.
Power factor is important to utilities who deliver electrical power to customers. For two loads that require the same level of real power, the load with the better power factor actually demands less current from the utility. A load with a 1.0 power factor requires the minimum amount of current from the utility. Utilities may offer a reduced rate to customers with high power factor loads.
A poor power factor may be due to a phase difference between voltage and current. Power factor can also be degraded by distortion and harmonic content of the current. In some cases, distorted current waveforms tend to increase the harmonic energy content, and reduce the energy at the fundamental frequency. For a sinusoidal voltage waveform, only the energy at the fundamental frequency may transfer real power to a load. Distorted current waveforms can result from non-linear loads such as rectifier loads. Rectifier loads may include, for example, diodes such as LEDs, for example.
LEDs are widely used device capable of illumination when supplied with current. For example, a single red LED may provide a visible indication of operating state (e.g., on or off) to an equipment operator. As another example, LEDs can be used to display information in some electronics based devices, such as handheld calculators. LEDs have also been used, for example, in lighting systems, data communications and motor controls.
Typically, an LED is formed as a semiconductor diode having an anode and a cathode. In theory, an ideal diode will only conduct current in one direction. When sufficient forward bias voltage is applied between the anode and cathode, conventional current flows through the diode. Forward current flow through an LED may cause photons to recombine with holes to release energy in the form of light.
The emitted light from some LEDs is in the visible wavelength spectrum. By proper selection of semiconductor materials, individual LEDs can be constructed to emit certain colors (e.g., wavelength), such as red, blue, or green, for example.
In general, an LED may be created on a conventional semiconductor die. An individual LED may be integrated with other circuitry on the same die, or packaged as a discrete single component. Typically, the package that contains the LED semiconductor element will include a transparent window to permit the light to escape from the package.
The present invention is provided to solve these and other issues.